1. Technological Field
The invention relates to a controlled deflection roll having a rotatable roll shell supported in a pressing plane in relation to a non-rotatable carrier by a row of neighboring hydraulic support elements, wherein the support elements can be supplied by infeed lines from the carrier with hydraulic pressurized medium generating a pressing force, and wherein there is provided a control device by means of which only a selectable part of neighboring support elements are supplied with pressurized medium.
2. State of the Art
One such roll is known, for instance, from the Swiss Patent No. 610,991, granted May 15, 1979 and serves for the pressure treatment of material webs, for example, for pressing paper-, cardboard-, textile- or other fiber material webs, for the rolling of metal foils or sheets, for the manufacture of plastic foils or as the pressing device of rotary printing machines. By means of the hydraulic support elements there can be produced an adjustable or regulatable pressing force upon the material web. By means of the control device, which can comprise, for instance, partition walls which are displaceable in the axial direction of the roll or an alterable or exchangeable mounting element in the carrier, it is possible to change the working width of the roll, that is, the number of simultaneously impinged neighboring support elements in the axial direction of the roll and to accommodate such to the width of the material web.
What is disadvantageous for rolling apparatuses working with such type rolls is that directly at the edges of the processed material web there can arise, for different reasons, an excessive compression, known as edge compression, which renders unusable a relatively large part of the marginal portions of the material web and sometimes requires appreciable cutting.
In German Patent No. 2,325,721, published Sep. 18, 1975, it is known, on the other hand, to overcome or compensate this excessive edge compression by support elements at the ends of the roll shell which are effective in a direction opposite to the pressing direction. What is here disadvantageous is that by virtue of these so-called counter support sources the entire pressing force effective in the pressing plane and thus the line force is altered, requiring a complicated regulation. Additionally, the counter support sources are only effective when they are arranged in the direct neighborhood of a guide device of the roll shell, which stabilizes the cross-section of the roll shell at this location and prevents a deformation of the cross-section. Upon undertaking a desired adjustment of the working width of such a roll,--which is not as such contemplated by the patent--, such counter support elements must, however, be provided directly neighboring the edges of the material web. At a certain distance from the ends of the roll shell, where there are provided the guide devices, such counter support sources become, however, ineffective due to the shell deformation of the roll shell which here becomes effective, so that the excessive edge compression no longer can be eliminated or compensated with a certain reduction in the working width.